Semiconductor logic devices including a microprocessor and semiconductor memory devices represented by a DRAM are inevitable as a central processing unit, an internal memory or an external memory of a computer and the like. In the process for producing such a large-scale integrated circuit, development of wiring technique for connecting several million to several ten million semiconductor transistors in one chip with high reliability is very important.
At present, DRAM's of 16 megabits using wiring layers having a width of 0.7 to 0.8 .mu.m and composed of an aluminum alloy material obtained by adding a small amount of silicon (Si) or a small amount of silicon and copper (Cu) to aluminum (Al), are ready for full-scale mass production.
These wiring layers are produced by forming a thin film of about 1 .mu.m in thickness on a silicon wafer by sputtering and forming a minute wiring pattern to the thin film by lithography. In producing these wiring layers, an Al-Si alloy target containing about 1 wt. % of Si or an Al-Si-Cu alloy target containing about 1 wt. % of Si and about 0.5 wt. % of Cu is used.
With the recent development of advanced large-scale integrated circuits following DRAM's of 64 megabits and with the recent development of wiring layers having a narrower width (e.g., 0.3 to 0.6 .mu.m) aimed at increasing the integration and the performance of semiconductor integrated circuits, a wiring technique having higher reliability has been demanded.
Al-Si alloy wiring layers or Al-Si-Cu alloy wiring layers used at present, however, have low reliability because an additive such as silicon precipitate during the manufacturing process and remains on the circuit, or breakage of wire is frequently caused thereby.
The breakage of an aluminum wire is ascribed to phenomena called electromigration and stress migration. The electromigration is a phenomenon in which metal ions are moved in wiring in accordance with an electric field by electric currents in the wiring and this effect causes voids on the grain boundary, thereby resulting in breakage of the wire. The stress migration is a phenomenon of breakage of wire caused by which the tensile stress is produced on the aluminum wire in accordance with the difference in the thermal expansion between the aluminum wire and the barrier film of SiN or the like laminated, thereby producing voids on the grain boundary.